SCJP6 regex issue
\d* matches 0 or more digits. So, it will even match empty string before every character and after the last character. First before index 0, then before index 1, and so on.
So, for string ab34ef, it matches following groups:
Index Group
0 "" (Before a)
1 "" (Before b)
2 34 (Matches more than 0 digits this time)
4 "" (Before `e` at index 4)
5 "" (Before f)
6 "" (At the end, after f)
If you use \\d+, then you will get just a single group at 34.